Structure and Phase Composition of Surface Restoration Layers in Gamma Titanium Aluminide Alloy Ti–44.5Al–2V–1Nb–2Cr–0.1Gd Obtained by Selective Electron Beam Melting and Post–Processing

Abstract The formation of the structure and phase composition in ~1000 µm thick restoration layers deposited by selective electron beam melting (SEBM) on artificial surface defects in cast and wrought workpieces made of a new heat-resistant alloy based on titanium aluminide γ-TiAl grade VIT7L (Ti–44.5Al–2V–1Nb–2Cr–0.1Gd, at.%) has been studied. It has been established that a specific three-phase (γ + α2 + β / B2) structure with columnar grains is formed in the repaired layers, the grain length reaching 270 μm (in the layers on cast base material) and 250 μm (on wrought base material). The most optimal technological SEBM parameters (EL = 285 J / m, I = 9.5 mA, v = 2 m / s) ensure the absence of fusion faults in the layers and a residual porosity of less than 0.5 vol.%, with Al losses of no more than 1 at.% with moderate structural heterogeneity. It has been shown that post-processing treatment including hot isostatic pressing (HIP) and heat treatment (HT) gives the opportunity to obtain defect-free, almost homogeneous material in the area of repair impact, with an average size of (γ + α2) colonies of no more than 150 μm (for cast base material, after HIP and HT) and no more than 80 μm (for wrought base material, after HT), with a minimum thickness of the transition zone not exceeding 500 μm.